Renal disease is a major health problem throughout the world. Prominent ones are diabetic nephropathy, various forms of hereditary nephritis, and immune-mediated nephritis, which impair the ultrafiltration function of the renal glomerulus and lead to end-stage-renal failure. The pathogenesis involves molecular alterations in the basement membranes that separate the glomerular compartments. In the last decade a family of collagen IV networks have been discovered, that are essential for glomerular function and which are directly involved in the pathogenesis of certain diseases. The general premise underlying this project is: the development and maintenance of glomerular function requires the temporal/spatial expression of collagen IV networks that provide mechanical strength to the compartments and selectively interact with cell-surface receptors influencing cell behavior. The goal is to define fundamental mechanisms, at the atomic, molecular and cellular levels, that contribute to network function. This objective will be achieved by the pursuit of four specific aims that address the molecular identity of sites on networks that confer stability and binding to integrin receptors that mediate biological function. Three distinct domains of two different networks, an a1.a1.a2 and an a3.a4.a5 network, will be investigated to define specificity of binding to integrins of various glomerular cell types. Emphasis will be placed on the ancient multi-functional noncollagenous (NC1) domain which acts as a molecular "Velcro" for binding chains for triple-helix assembly, binding triple-helical molecules for network assembly, and binding networks to cells through integrin receptors. The experimental strategies utilize state-of-the-art technologies of structural biology and proteomics mass spectrometry, x-ray crystallography and surface plasmon resonance) in combination with classical cellular and molecular methodologies.